The present invention relates to articles comprising a substrate, a release liner and an adhesive layer sandwiched between the substrate and release liner and methods of manufacturing such articles. The release liner has a relatively high coefficient of friction and has shrinkage properties that are substantially the same as or greater than the substrate. The article exhibits good roll stability, being substantially free of defects when supplied in a roll form.
A variety of articles, such as tapes (e.g. packaging, automotive, medical), labels, sheeting for traffic control signage, and commercial graphic films for advertising and promotional displays comprise an adhesive coated substrate (eg. backing, sheeting) having a release liner temporarily covering the adhesive layer. These articles are typically supplied as sheets or in a roll form. Provided that proper tensioning is employed, it is typically unproblematic to convert dimensionally stable substrates in combination with dimensionally stable release liners.
On the other hand, flexible plastic substrates tend to be much more difficult to convert, often exhibiting roll defects such as wrinkles and buckling. Many of these defects occur during the manufacturing process and are primarily process related. Other defects, appear after manufacturing and prior to use and thus are related primarily to the physical properties of the materials employed as a function of storage conditions as well as interactions of these materials with each other.
WO 99/14281 relates to a release liner for use with a pressure sensitive adhesive. The release liner includes a film of a thermoplastic elastomeric olefin. At p. 14, this reference states that xe2x80x9cThe release liner of the invention preferably exhibits substantially no shrinking or buckling when brought to room temperature after being exposed to an elevated temperature for an extended period of time. A preferred liner exhibits substantially no shrinking or buckling when brought to room temperature (i.e., about 20-25xc2x0 C.) after being exposed to a temperature of about 90xc2x0 C., more preferably about 120xc2x0 C., and most preferably about 150xc2x0 C., for a period of about one-half hour, more preferably about one hour. Shrinking and buckling can be avoided by selecting a release liner having thermal expansion and contraction coefficients substantially similar to those of the intended substrate.xe2x80x9d
It is generally known and appreciated by those of ordinary skill in the art that a combination of substrate, adhesive and release liner that exhibits good roll stability can exhibit roll defects upon replacing either the substrate or the liner with a different material. For example, xe2x80x9cScotchlite High Intensity Grade Reflective Sheeting Series 3870xe2x80x9d, commercially available from Minnesota, Mining and Manufacturing Company (xe2x80x9c3Mxe2x80x9d), St. Paul, Minn. employs an xe2x80x9cencapsulated lensxe2x80x9d type retroreflective sheeting, generally prepared as described in U.S. Pat. No. 4,025,159. This sheeting employs a polymethylmethacrylate cover film in combination with a thermally crosslinked adhesive and a release liner having a relatively low coefficient of friction. Although this combination of substrate, adhesive, and liner exhibits good roll stability, roll defects became evident in attempting to replace the liner with an alternative material.
The present inventors have discovered that xe2x80x9cshrinkagexe2x80x9d is an important factor in preventing roll defects that occur post-manufacturing during storage. Accordingly, an object of the present invention is to provide an article comprising an adhesive sandwiched between a substrate and release liner that exhibits good roll stability. Another object of the invention is to provide a retroreflective article comprising an adhesive sandwiched between a substrate and release liner wherein the article or the adhesive in combination with the liner can be subjected to electron beam radiant energy and maintain sufficiently low release values.
In one aspect, the present invention is an article comprising an adhesive layer disposed between a substrate and a liner. The liner is releasably adhered to the adhesive and has a relatively high coefficient of friction, of at least about 0.30. The substrate exhibits shrinkage and the liner exhibits a shrinkage ranging from substantially the same as to greater than the substrate.
The coefficient of friction of the liner is preferably at least about 0.40, more preferably at least about 0.45, and most preferably at least about 0.50.
The substrate is preferably a film comprising acrylic, poly(vinyl chloride), poly(vinyl fluoride), polyurethane, polyolefin, polyester, and combinations thereof with acrylic such as polymethymethacrylate and polyolefin being most preferred.
The force per unit width of the substrate is preferably at least two to three times greater than the liner. In preferred embodiments the force per unit width of the substrate is at least 1xc3x97103 Newtons/cm greater and more preferably 1xc3x97104 Newtons/cm greater than the liner.
The adhesive is preferably heat-stable and preferably crosslinked such as acrylate based pressure sensitive adhesive compositions. The preferred adhesive compositions are crosslinked with an electron beam radiant energy source and thus are substantially free of photoinitiator.
The substrate is preferably retroreflective sheeting such as enclosed-lens, encapsulated lens, and cube-corner type retroreflective sheeting with encapsulated lens type being most preferred.
The release liner preferably comprises a backing and a release coating composition comprising a cure-on-demand moisture curable composition having reactive silane functionality. The moisture-curable release composition comprises a compound comprising molecules bearing reactive silane functional groups and an acid generating material that is free of ammonium salt.
In another aspect, the invention provides an article comprising an adhesive layer disposed between a retroreflective substrate and a liner, wherein the adhesive-facing surface of the liner has a coefficient of friction of at least about 0.30.
In another aspect, the present invention is a method of making an article comprising:
a) providing a substrate that exhibits shrinkage;
b) providing a liner that exhibits shrinkage ranging from substantially the same as the substrate to greater than the substrate and a coefficient of friction of greater than 0.30;
c) coating the substrate with an adhesive composition;
d) contacting the liner to the adhesive composition forming an article; and
e) winding the article into a roll.
In another aspect, the method of making the article comprises:
a) providing a substrate that exhibits shrinkage;
b) providing a liner that exhibits shrinkage ranging from substantially the same as the substrate to greater than the substrate and a coefficient of friction of greater than 0.30;
c) coating the liner with an adhesive composition;
d) contacting the substrate to the adhesive composition forming an article; and
e) winding the article into a roll.
In another aspect, the method of making the article comprises:
a) providing a substrate that exhibits shrinkage;
b) providing a first liner;
c) coating the first liner with an adhesive composition;
d) contacting the substrate to the adhesive composition;
e) stripping the first liner exposing the adhesive;
f) contacting the adhesive to a second liner that exhibits shrinkage ranging from substantially the same as the substrate to greater than the substrate and a coefficient of friction of greater than 0.30 forming an article; and
e) winding the article into a roll.
Each of these methods preferably further comprise exposing the adhesive to an electron beam energy source.